It is a standard laboratory procedure to measure and analyze the gases exhaled by laboratory animals, such as, rats to determine the presence of disease in the blood. Customarily, this has been accomplished by a gas washing procedure which involves directing the flow of exhaled gases through a liquid in order to capture some property present in the exhaled product. For example, measurement of the carbon monoxide level provides an indication of hepatic bilirubin production in the animal. The gas washing procedure entails the steps of drawing exhaled air from the cage, converting the carbon monoxide present in the air to carbon dioxide, then bubbling or washing the carbon dioxide through a bottle filled with a liquid, typically ethanolamine, for a predetermined time interval followed by measuring the amount of carbon monoxide recovered in the liquid. In the past this has required the tedious procedure of manually directing the gas into a succession of bottles over an extended time period. Continuous effort and supervision by an operator is required in order to obtain samples at timed intervals over periods as long as twenty-four hours. After each bottle is filled, it must be sealed and removed to an analysis chamber to evaluate the gases therein.
More recently, the procedure of collecting fluid samples for various purposes, not necessarily involving gas washing, has been facilitated by the use of automated apparatus for collecting one or a plurality of gas samples into bottles for analysis. For example, U.S. Pat. No. 3,362,222 to W. K. Johnson et al teaches the use of a plurality of evacuated bottles connected to a fluid stream by normally closed tubes; solenoid-actuated valves are automatically and sequentially opened at timed intervals to allow fluid to flow through the tubes and into the bottle. The apparatus described in U.S. Pat. No. 3,043,145 to H. T. Hoffman also utilizes solenoid valves to control sampling of fluid: the fluid to be analyzed is drawn from different sources through sample lines into a manifold by a washer pump, and after washing, the pump delivers the sample to a gas analyzer. U.S. Pat. Nos. 4,090,392 to I. I. Smith et al and 3,369,405 to R. R. Galegar are directed to computer controlled systems for sampling fluid from different locations, utilizing solenoid valves to sequentially or simultaneously open a number of sample lines. Despite advantages such systems might make in a gas washing application, there remains a need for an apparatus which is capable of improving the efficiency and accuracy of the gas washing procedure by providing a compact system for collecting gas samples over extended time periods and which requires little or no observation or active participation by the laboratory technician.